This invention relates to a flotation apparatus and method for removing contaminants from wastewater. It is particularly well suited to removing grease particles and other suspended solids from packinghouse effluent by introducing into the packinghouse effluent a gas-containing liquid which has or forms microbubbles which attach themselves to the suspended solids, floating the suspended solids to the liquid surface for removal.
Inasmuch as gravitational separation cannot effectively remove fat and tissue particles which have a density similar to that of water, microbubble flotation processes have been used in the past for treatment of packinghouse effluent. Such apparatus has included a large tank which provides a flotation chamber, a feed line introducing the packinghouse effluent into one end of the tank and a baffle and weir structure leading to an effluent discharge chamber at the opposite end of the tank. Aerated liquid is introduced into the feed line to provide millions of microbubbles having a diameter in the general range of 100 microns. These minute bubbles ascend slowly, attaching themselves to suspended particles, buoying the suspended particles to the surface of the treatment tank where they are removed by paddles on a skimming chain. The clarified liquid then passes under a baffle and over a weir into an effluent chamber. A portion of the clarified liquid is withdrawn, aerated and recycled to the feed line as the aerated liquid.
The present invention involves an improved apparatus and method for introducing the aerated liquid into the wastewater to form an intimate mix of the incoming contaminated wastewater and the aerated liquid. Further, the invention pertains to the structure for distributing the intimate mix within the flotation chamber to optimize contaminant removal. The supply means for introducing the gas containing liquid into the wastewater includes a pair of discharge openings immersed in the wastewater and oriented in spaced opposed mutually confronting relationship whereby streams of gas-containing liquid emerging from the openings collide to create an area of high turbulence and produce an intimate mix of gas-containing liquid and wastewater. Preferably, the gas-containing liquid is produced by passing a gas injected into a liquid stream through a motionless mixer provided with stationary internal vanes which produce shear forces in the gas-containing liquid stream. Adjacent vanes in the mixer are twisted in opposite directions to move the gas-containing liquid stream alternately in a left-hand helical path and a right-hand helical path. To distribute the intimate mix of wastewater and gas-containing liquid in the tank, a transverse baffle is aligned with and located downstream of the opposed discharge openings, the transverse baffle is oriented transversely to the path from the inlet means to the effluent discharge means, and horizontal baffles are vertically spaced from the transverse baffle to aid in directing the flow of the mix horizontally across the width of the flotation chamber. At spaced locations along the length of the flotation chamber, there are panels providing sets of vertical vanes which reduce the transverse flow of liquid in the tank and minimize turbulence after the desired distribution of the mix is attained.
The invention may be accomplished by a wide variety of devices and techniques, a preferred example of which is shown and described in this specification.